This invention relates to packing materials, and more particularly, to packing cells positioned in a packed tower for promoting gas-liquid and liquid-liquid contact.
Gas-liquid and liquid-liquid mixing towers are used in industrial processes for a variety of purposes. In an absorption or scrubbing operation, for example, one or more constituents of a mixture of gases is removed by contacting the mixture in a tower with a liquid capable of dissolving the gases. In a stripping operation, a dissolved component is removed from a liquid stream by volatilization into a gas stream injected in a tower. Distillation of multicomponent feeds also transpires in a contacting tower.
In contacting towers, various means are used to promote contact between the components being mixed. One such means is a bubble-cap plate, which is a horizontal deck with a large number of chimneys over which circular or rectangular caps are mounted to channel and distribute gas through the liquid. Liquid flows by gravity downward from plate to plate through separate passages, called downcomers. Each bubble-cap plate must be custom made for each installation, however, increasing the cost of such plates. Channeling is frequently a problem with bubble-cap plates since the liquid flows through the channels formed by the downcomers. Since large flat areas are positioned in the path of the moving fluids, a large pressure drop occurs, resulting in significant energy losses and inefficiency in operation.
A sieve plate can also be positioned in a tower to promote gas and liquid contact. A sieve plate is a horizontal deck with several round holes for mixing the gas and the liquid. Sieve plates have several drawbacks, however. They have a restricted operating range since the plates "flood", i.e., the amount of liquid flowing into the tower exceeds the amount which can flow through the sieve plates. Sieve plates also "weep" relatively easily, i.e., the liquid in a gas-liquid mixture flows downwardly through the holes in the plates. Each sieve plate must be made for a specific installation; hence, standardization in manufacturing is not generally feasible. Sieve plates, like bubble-cap plates, produce significant pressure drops in the fluids flowing through the mixing tower, because they have large, flat surface areas disposed in a rapidly flowing fluid stream. Another drawback of sieve plates is that they can easily clog and corrode, depending on the composition, and then must be either replaced or cleaned, thus increasing the costs associated with their use. Non-corroding materials for sieve plates are often quite expensive.
Packed columns have also been developed to promote fluid contact. A packed column has a succession of beds made up of several small solid shapes through which the fluids flow in tortuous countercurrent paths. The packing materials assume various shapes to promote mixing. These shapes have recognized names, such as Raschig rings, Lessing rings, Berl saddles, Prym partition rings, and double-turn spirals. Polyhedral cubes have been suggested for forming a bed in a packed tower. These polyhedral structures must be carefully placed in the tower in an interlocking relationship to mix the fluids; otherwise, the liquids tend to flow in channels through the tower, thereby preventing good mixing. Spheres have also been suggested to overcome the problems relating to the orientation of the packing materials. The spheres must be individually prepared for each installation, and standardization in manufacture is difficult. Hollow perforated spheres have also been suggested, but, again, the surface area for fluid contact cannot be easily modified. And, significant pressure drops are likely in prior arrangements.
Accordingly, a need thus exists for novel packing cells which cooperate in interlocking relationship to prevent channeling in a packed mixing tower. Packing cells which induce a minimal pressure drop are needed as well. A need also exists for a packing cell whose surface area can be easily altered to accommodate different fluid mixing conditions, permitting standardization in manufacture and hence, reducing costs.